Ocular imaging is commonly used both to screen for diseases and to document findings discovered during clinical examination of the eye 1. The most common type of photographic ocular imaging is digital photographic imaging of the retina 10. However, imaging of the anterior segment 15 of the human eye 1 is increasingly common, to document pathology of the anterior segment 15, particularly in conjunction with documentation in electronic medical records. Current photographic imaging of the anterior segment 15 is performed primarily using non-contact digital photography. Anterior segment 15 photography has also been performed using contact imaging systems such as the RetCam by Clarity Medical, which was designed primarily for retinal imaging, but which may be used for anterior segment 15 photography as well.
Anterior segment 15 photography may be used to image various ocular structures, including but not limited to: the iridocorneal angle 12; the iris 6; the anterior chamber 17; the crystalline lens 5 or an artificial lens implant; and the anterior vitreous 18.
Documentation of the iridocorneal angle 12 is particularly important in patients diagnosed with glaucoma; patients who are labeled as glaucoma suspects; patients with proliferative ischemic retinal diseases, such as proliferative diabetic retinopathy or central retinal vein occlusion; and patients with blunt traumatic injury to the eye 1. Abnormalities of the iridocorneal angle 12 require imaging with a gonioscopic optical system, since the angle 12 is obscured from direct view on clinical examination by total internal reflection of the cornea 3. Gonioscopic examination or imaging is defined as examination or imaging of the iridocorneal angle 12. In clinical practice, the iridocorneal angle 12 is most commonly visualized using a contact lens with multiple mirrors or prisms; the mirrors or prisms are positioned to avoid total internal reflection while providing views of the angle 12. In small children, ophthalmologists sometimes use a Koeppe direct gonioscopic lens, which allows for visualization of the angle 12 without the assistance of mirrors or prisms.
During clinical examination of the iridocorneal angle 12 with a gonioscopic lens, indentation gonioscopy may be performed. Indentation gonioscopy is a technique of examining the iridocorneal angle 12 while gently applying and releasing pressure against the cornea 3 using the gonioscopic lens. The pressure against the cornea 3 causes an elevation of the intraocular pressure, which consequently changes the anatomic configuration of the iridocorneal angle 12. Indentation gonioscopy is therefore a dynamic examination, which is best captured by digital video rather than still digital images, but which may be captured by still images under varying degrees of pressure.